The present invention relates to pulverized coal furnaces designed as direct fired systems and more particularly to an apparatus and method for maintaining the heat input to the furnace at the design level when firing coal of lower grade than the pulverizers were designed for. Specifically, this invention is directed to an apparatus and method for injecting a dense phase pulverized coal stream into the main coal/air stream discharged from the pulverizer.
During the past few years there has been an increase in the use of western coal in steam generating units because of its ready availability and low sulfur content. Western coals are typically of the bituminous and lignite ranks and have lower heating values, lower grindability, and higher moisture content that their eastern bituminous coal counterparts. Since pulverizer capacity, i.e., the pounds per hour of coal discharged from the pulverizer, is directly dependent upon the grindability and moisture content of the coal, the capacity of a given pulverizer is substantially less when grinding a western coal than when grinding an eastern coal. Additionally, pulverizer output, i.e., the heat content of the coal discharged from the pulverizer to the burners, is even further decreased as a result of the pulverizer discharging less pounds of the lower heating value western coal than of the higher hearing value eastern coal. Accordingly, a utility would generally experience a decrease in generating capacity when switching from eastern coal to western coal.
The typical solution to the problem is to make major modifications in the steam generating unit by adding an additional pulverizer and an additional level of burners to the furnace in order to regain the generating capacity lost when switching to the western coal. However, such major changes necessitate that the unit be taken out of service for a significant period of time resulting in a substantial loss of generating capacity to the utility. In many cases, it is nearly impossible to add an additional pulverizer to a steam generating unit simply because of space limitations in the immediate vicinity of the furnace.
Therefore, a need exists for an apparatus and method of providing supplemental pulverized coal to the steam generator for load regain which permits an additional pulverizer to be remotely located, eliminates the necessity of adding an additional elevation of burners, and minimizes the downtime required for the change to be made.